Strange fix for a strange problem

I am really puzzled by this.

Diesel Focus Econetic 5dr 1.6L Born 2010, had 62 miles on the clock when we bought it, mileage we do is about 8.5k p/a
Driven gently, 55,000 miles on the clock, regularly serviced, on a run gives 70mpg

Stop_Start stopped working some years back, appearing every now and then but rarely, and started again with a new AGM Battery and fresh alternator last month.
I assumed the failure was connected to a worn out battery that couldn't do the volts.
Then it stopped working again a week ago.
We had the usual annual "Oil Service" warning which I reset with the accelerator and brake sequence.
Stop_Start still didn't work.
Today, on a hunch, I disconnected the battery negative terminal for fifteen minutes. I wondered if, like a home computer, sometimes you just need to turn the thing off and on again.
How right I was.
Now Stop_Start works normally again.

My questions:- (1) Why?  (2) Is there a better way to reset without undoing a terminal? (3) Does all this indicate a bigger problem?

Any ideas gratefully received